A vibratory feeding apparatus may comprise a container in the form of a rotary vibration bowl and a linear feeder in the form of a vibration track. They can be found in industry for conveying and orientating components, for instance electronic components, which are sorted from a pool of randomly oriented components during mass production. They are different from belt conveyers in that vibratory feeding apparatus use small vibrations to transfer components in a step-wise manner. Due to its simplicity and lack of moving mechanical parts, the vibratory feeding apparatus can provide a cleaner and more reliable way of conveying small components. Thus, there are large numbers of vibratory feeding apparatus developed for conveying small components in different industries.
A vibratory feeding apparatus generally involves four main mechanical modules: a bowl or track for orientation and sorting, a hopper for refilling the bowl or track, linear and/or rotary vibrator modules for exciting the bowl, track and/or hopper to vibrate, and a platform for vibration isolation.
The linear or rotary vibrator module generally excites the bowl or track to undergo vibration with a single frequency. The vibrator module comprises a movable block that transmits vibration to the bowl or track, an actuator that provides excitation forces to the movable block, and a spring-mass system that determines the vibration frequency of the vibrator and the conveyance direction. The vibrator module traditionally uses an electromagnetic solenoid, such that the force-displacement relationship of the vibrator module is non-linear in nature. The force from the solenoid accelerates the bowl or track to vibrate and the components placed on the bowl or track experience acceleration. The resultant acceleration has both vertical and horizontal components. When the vertical acceleration field is slightly larger than the gravitational field, the components are lifted off the bowl or track surface and are projected forward due to the horizontal acceleration component.
U.S. Pat. No. 6,206,180 entitled “Vibratory Parts Feeder” discloses a vibratory feeding apparatus which uses two sets of electromagnetic coils to generate vibration in vertical and horizontal directions respectively to create vibratory motion for a bowl feeder. An elliptical motion stroke is employed by changing the current phases of its motors in order to achieve a higher feeding speed.
U.S. Pat. No. 6,705,459 entitled “Two-Way Vibratory Feeder” discloses two-way vibratory feeding utilizing motor exciters. The bidirectional mechanism is constructed with different operational resonant frequencies. It can control the components on the surface of the feeder to move back and forth along X and Y axes on a horizontal plane independently.
Generally, since solenoids are used as electromagnetic actuators and the force-displacement characteristic of a solenoid is non-linear, the force input to the vibrator module thus varies with both the driving current and the displacement. Driving of the solenoid using a sine wave signal source also introduces a non-linear force which contains many different frequency components other than the desired excitation frequency to the vibrator module. Undesirable frequency components will cause unwanted motion of the components being transferred using the vibrator module. It may also generate noise from abrupt changes in the driving signal source.
Another vibrator module uses a square waveform as the driving signal source. Apart from the multiple frequency components generated by the vibrator module, the vibrator module also generates noise as a result of abrupt changes in force inherent in a square waveform. It is thus preferable to develop a vibrator module with linear driving actuators so that the vibrator module can vibrate in a purer single frequency.
Certain state of the art vibrator modules use flexible piezoelectric elements as actuators, which provide linear forces to the vibrator module. The flexible piezoelectric elements are formed by bonding piezoelectric ceramic on a metallic or fiber-based composite substrate. As piezoelectric elements are compact and light, bowl or track designs using them are usually tidier and lighter. This also makes vibrator modules using piezoelectric elements more compact and much more space can be reserved for other functional modules. Moreover, the piezoelectric element is usually integrated to the spring of the vibrator module, and this makes the mass of the moving part of the vibrator module lighter and vibrator modules using piezoelectric elements can run at high frequencies.
However, since piezoelectric elements are made from the bonding of a piezoelectric ceramic on a metallic or fiber-based composite substrate, possible delamination may occur after repeated cyclic motion. Reliability of the piezoelectric element is thus a major problem for the vibratory feeding apparatus when it is operated in heavy volume production. It is thus advantageous to use a more robust actuation means that can operate in harsh conditions. Also, the cost of piezoelectric elements is usually higher than for solenoids.
Apart from nonlinear forces and lack of reliability of prior art vibration actuators, the designs of vibrator modules are usually limited to only linear or rotary agitation. Since there are many different vibratory feeder applications in the field, it is better to have a vibrator design which can easily switched between linear and rotary agitation. Also, this can help to standardize the parts required in inventory and make on-site maintenance easier. Where there are two separate systems produced respectively for generating rotary and linear motions, the two systems must be well-isolated so as not to adversely affect the respective motions. Further, there is a risk of jamming between the two systems when the two systems separately vibrate.
In view of the above mentioned shortcomings, it would be advantageous to design a vibrator which utilizes a linear actuator. Moreover, it is better to make the design common for both linear and rotary vibrators.